In regard to a camera module mounted in a recent mobile phone, focus is increasingly put on to promote low cost, small size, and reduction in thickness. In the camera module, a decrease in the light quantity of a peripheral portion of an image, partial coloring of an image or the like occurs depending on the optical performance of a lens. In regard to this phenomenon, the camera module performs image processing, such as shading correction or coloring correction. In recent years, many camera modules use a measure to increase the gain with respect to the output of an image sensor particularly in a low-illuminance environment as a countermeasure against degradation in sensitivity with the miniaturization of pixels.
In the image processing of the related art, predetermined luminance or color temperature is postulated, and adjustment corresponding to reduction in the light quantity of the peripheral portion or coloring is performed. As a method of adjustment, a method which uses a digital gain determined for each of a plurality of points of a screen or a digital gain determined by linear interpolation at a position between points, a method which uses a desired N-order function, and the like are known.
In the case of shading correction or coloring correction with predetermined luminance postulated, as the gain becomes larger in a low-illuminance environment, an adjustment error increases, and the precision of correction is lowered. In the case of shading correction aimed at low illuminance, an adjustment error due to the effect of a quantization error or the like increases in an environment which is brighter than the aimed illuminance. The imaging characteristic in the light-receiving surface of the image sensor changes depending on the wavelength of light, such that, when a color temperature varies, an error may occur in coloring correction.